重金属Hg^(2+)离子作用于PSII 23 kD外周蛋白的光谱学研究

Spectroscopic Study on the Interaction between Hg^(2+) Ions and 23 kD Extrinsic Polypeptide of Photosystem II

23 kD蛋白是光系统II(PSII)的外周蛋白,具有增加Ca2+和C l-的结合以维持放氧活性的作用。本文借助内源荧光光谱和紫外吸收差谱考察了23 kD蛋白与Hg2+的相互作用。所得结果表明:低浓度的Hg2+离子(<10μM)引起23 kD蛋白的荧光淬灭,淬灭程度与Hg2+离子浓度相关;进一步分析显示,Hg2+离子对23 kD蛋白色氨酸荧光的淬灭属于静态淬灭。紫外吸收差谱可以检测到明显的配体向金属进行电荷转移的谱带(LMCT band)。随着Hg2+浓度的增加,LMCT带的强度逐渐增强。分析显示23 kD蛋白只存在一类Hg2+离子结合位点。

23 kD protein ,one of the important extrinsic proteins of photosystem Ⅱ ,plays an essential role in the binding of Ca^2＋ and Cl^- and the activity of oxygen evolution of PSII. Interaction of 23 kD protein with mercury （Ⅱ） ions was studied by fluorescence spectroscopy of intrinsic tryptophan and ultraviolet （UV） differential spectrometry. On the interaction of 23 kD protein with mercury （Ⅱ） ions in low concentrations （ 〈 10 μM）, a quenching of fluorescence took place and exhibited the concentration-dependent pattern. During the binding process, a progressive increase in absorbance intensity of ligand-to-metal charge transition （LMCT） bands was observed with UV differential spectrometry,and the absorbance values of the LMCT bands increased as mercury （Ⅱ） ions concentration increased. Only one kind of mercury （Ⅱ） ion binding site existed in 23 kD protein.